1. Field of the Invention
This invention generally relates to printing machines, such as printers and typewriters, using a type wheel for printing characters which is rotatably housed in a cassette, and particularly to a structure for detachably supporting such a cassette-housed type wheel. The present invention also relates to a cassette for rotatably housing therein a type wheel, which may be detachably inserted into the type wheel supporting structure of a printing machine.
2. Description of the Prior Art
Printing machines using a type wheel for printing characters are well known in the art. In such wheel printers, several type wheels having different fonts may be selectively and detachably mounted in position for printing desired characters. A typical structure for detachably supporting such a type wheel, which is normally housed in a cassette, is disclosed, for example, in Japanese Patent Laid-open Publications Nos. 56-144968 and 56-144969. In the disclosed structure, a selection motor for driving to rotate a type wheel thereby having a selected type located at a predetermined printing position is mounted a on motor supporting frame which is provided to be located closer to or separated away from a platen roller. Also provided is a spring which is connected to urge the supporting frame in the direction directed away from the platen roller; on the other hand, also provided is an operating lever which causes, when operated manually, the supporting frame to be located closer to the platen roller against the force of the spring. A holding member is also provided for holding the supporting frame at that location closer to the platen roller.
The prior art structure for supporting a type wheel housed in a cassette as described above is extremely complicated in structure and thus difficult to assemble and expensive to manufacture. Moreover, a replacing operation of type wheels in such a prior art structure cannot be carried out smoothly and requires skills and experiences.